The invention relates generally to a method and device for correcting vision and more particularly to the application of laser energy or ultrasound to treat conditions such as, for example, presbyopia, hyperopia, primary open angle glaucoma and ocular hypertension.
The ability of an eye to switch focus from a distant image to a near image depends on the ability of the eye to change its shape. Specifically, certain structures of the eye, such as, for example, the lens, must change its shape or position so that proper focus of light on the retina is achieved. A number of these structures are under muscular control.
The shape of the lens is affected by muscular action. The lens is held in place behind the iris by zonules or suspensory ligaments, which attach to the wall of the eye at the ciliary body. When the ciliary muscles contract, tension on the zonules increases, which allows the lens to increase its curvature and assume a more spheric shape because of its elastic properties.
When light from a distant visual image enters the normal emmetropic eye with a relaxed ciliary muscle, the target is in focus on the retina. However, if the eye is directed at a nearby visual target, the light is initially focused behind the retina, i.e. the image at the retina is blurred, until accommodation occurs. The image is sharpened when the lens becomes thicker with a steeper central curvature because of contraction of the ciliary muscles, resulting in a decreased diameter across the lens as well as its suspensory connections to the wall of the eye via the zonular fibers which become relaxed, allowing the lens to achieve this more spherical shape as needed.
Accommodation refers to the ability of the eye to change its focus. Accommodation is measured by the accommodative amplitude, that is, the power, measured in units called diopters (D), that the lens can vary from the non-accommodative state to a full accommodative state. For example, in accommodation for near vision, the lens increases its curvature, and as such, the amplitude of accommodation increases.
The lens continues to grow throughout an individual""s lifetime. The rate of lens growth is usually about 20 to 30 microns per year. As such, the lens diameter increases over time and this increase has been correlated to a decrease in accommodative power and thus, a decrease in the ability of the lens to focus on near images. The gradual loss of accommodative power with age means that individual""s ability to focus on near images declines over time. When the near point of accommodation has receded beyond a comfortable distance, the individual is said to have a condition called presbyopia.
In addition to vision impairment, conditions like presbyopia, also cause eye strain, experienced variably as fatigue, pressure behind the eye, brow ache, and generalized discomfort. To focus on an object, individuals with accommodative impairments hold objects at increasing distances from the eye. Eventually, prescription vision correction in the form of reading glasses, bifocals, trifocals, or some form of compromise between distance focus in one eye and near focus in the other, commonly known as monovision, is implemented. Typically, about 3 diopters of accommodation is necessary to read at a comfortable, close-up distance, and about 6 diopters is necessary to permit reading for extended lengths of time without premature fatigue and discomfort setting in.
Recovery of accommodative ability for conditions like presbyopia may allow an individual to have focused near vision. Preferably, such a method would be noninvasive and repeatable to allow for retreatment, should age and continued lens growth again cause an insufficient amplitude of accommodation.
Accordingly, there remains a need for a safe, effective, non-invasive method of altering the eye to correct ophthalmic conditions, such as, for example, presbyopia, where such treatment lessens or eliminates the need for auxiliary spectacle lenses and avoids the common undesirable side-effects associated with traditional eye surgery. There is also a need for an apparatus designed to practice this method.
It is an object of the invention to induce controlled cellular damage or biochemical changes to tissues that control the accommodative apparatus in order to effect biochemical changes and a healing response in a human eye that counteract the effects of presbyopia.
It is another object of the invention to increase the tension on the zonules through directly or indirectly increasing tension of surrounding tissues in a therapeutically effective amount sufficient to reverse the affects of presbyopia.
Another object of the invention is to slow the growth rate and/or stretch rate of target tissues so that the onset or progress of presbyopia is sufficiently retarded.
Another object is to alter the elasticity of the lens capsule so that the onset and progress of presbyopia is sufficiently retarded.
It is also an object of the invention to induce controlled cellular damage to target tissues to restore zonular tension so that presbyopia is sufficiently reversed to be clinically beneficial.
It is yet another object of the invention to preemptively combat presbyopia by prophylactically treating target tissues so that presbyopia may be sufficiently prevented.
These and other objects, advantages, and features of the invention will become apparent to those persons skilled in the art upon reading the details of the device and method as more fully described below. Other objects and advantages may become more apparent to those skilled in the art upon reviewing this summary of the invention, in view of the description of the preferred embodiment.